1. Field of the Invention
This invention relates to internal combustion engines and, more particularly, to internally insulated manifolds for said engines.
2. Description of the Prior Art
There has been considerable development work on engine exhaust manifolds that are internally insulated with the view to maintaining the manifold housing temperature below a predetermined limit. One such manifold has a cast ferrous inner conduit surrounded by insulation, which in turn, is covered by a cast outer manifold. This construction is substantially impractical in that the inner casting will rupture due to thermal fatigue since no provision has been made for relieving the thermal stresses.
In another construction, hard alumina and silica are cast with metallic fibers embedded therein to form a liner. The housing is cast about the liner. The resulting manifold is impractical since it has been found that alumina is subject to surface fatigue due to temperature cycling which produces a fine dust that goes out the exhaust. Aside from the dust problem, it has been found that the structure will not hold up over a period of time.
A third construction calls for an inner liner of refractory fibers and refractory binder with a cast metal manifold on top of it. The cast metal penetrates the insulation during the casting. In time, with the insulation rigid, the outer casting ruptures and, with the insulation not rigid, the insulation fatigues out.
And still another construction has a thermally insulating core of relatively fragile material surrounded by a softer cushioning material and a cast metal sheet on the outside. There is no provision for preventing thermal fatigue of the liner and, therefore, the solution is undesirable.